The invention relates generally to power-driven conveyors and, more particularly, to modular belt conveyors having retractable flight members.
Many conveying applications require that conveyed articles be spaced apart on a conveyor belt. For example, merging two or more flows of articles into a single file without collisions is a common requirement. One conveyor used to accomplish this without slowing the belt or using complex sensors and external spacing bars is described in co-pending U.S. patent application Ser. No. 11/610,737, filed on Dec. 14, 2006, by the applicant of this application. The disclosure of that application is incorporated herein by reference. The conveyor includes a conveyor belt, belt rollers, and flights. Lower surfaces on the rollers engage a roller-engagement surface below the belt. Upper surfaces of the rollers define a plane above the belt. As the belt advances, the rollers roll on the roller-engagement surface and rotate to move an article supported on the rollers forward along the plane. The flights, which are spaced apart along the length of the belt, include cams that engage a cam surface below the belt to impart a moment on the flight and projections that respond to the moment by rotating from a retracted position to an extended position blocking the further advance of an article propelled forward. The cam-actuated flights, in conjunction with the article-accelerating rollers, cause conveyed articles to be staged at known locations on the belt for proper merging. The flights assume a retracted position as they return from the returnway before they encounter the cam surface. A conveyed article resting atop a retracted flight before it is raised to the extended position prevents the flight from popping up by cam action until the article is pushed clear of the flight by the rollers. Then the cam pops the unencumbered flight up to the extended position. When a flight is weighted down, its cam merely slides along the cam surface.
This device works well in most applications. But, in the case of lightweight articles, such as envelopes, for example, the cam-actuated flights have enough torque to rotate the retracted flight with a lightweight article atop it to the extended position. The lightweight article may be left stranded, leaning from the top of the flight without enough frictional contact with the belt rollers to clear the article from the flight. Consequently, the regular positioning of articles atop the belt for reliable merging or other applications requiring uniform product spacing is disrupted.